doc-guide:kernel-doc.rst: Reference to foobar

In the Function documentation Section of kernel-doc.rst
there is a function_name() function as an example for
how to make a comment about a function.

But at the end of that example there is a reference to foobar
instead of function_name.

I think that should rather be function_name, because that
was the placeholder the whole example was using.
Signed-off-by: Joris Gutjahr <joris.gutjahr@gmail.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

Documentation/doc-guide/kernel-doc.rst

@@ -77,7 +77,7 @@ The general format of a function and function-like macro kernel-doc comment is::
    * Context: Describes whether the function can sleep, what locks it takes,
    *          releases, or expects to be held. It can extend over multiple
    *          lines.
-   * Return: Describe the return value of foobar.
+   * Return: Describe the return value of function_name.
    *
    * The return value description can also have multiple paragraphs, and should
    * be placed at the end of the comment block.